Caroline Kennedy got what is presumably her first look at a crack rock yesterday — and she and her fellow jurors on a small-time Harlem buy-and-bust trial didn’t seem too impressed.

“I’m now going to show you what’s been offered into evidence as People’s Exhibit 7,” a prosecutor announced before pulling two double-bagged crack rocks out of an evidence box in the Manhattan Supreme Court trial.

Kennedy — chosen this week as juror No. 7 — squinted briefly at the tiny, pinkie-nail-sized bits of cocaine, more like pebbles than rocks.

The former first daughter has since Monday been sitting in judgment of Nelson Chatman, 31, who faces a six-year minimum prison sentence if convicted of selling $20 in crack to an undercover cop near Harlem River Park last December.

Chatman, 31, has been sporting a new haircut since Thursday, when the veteran thief and drug dealer infuriated the trial judge, Manhattan Supreme Court Justice Richard Carruthers, by refusing to come to court in the morning so that he could instead sit in a barbers chair in Rikers.

Yesterday, a judge two floors down, Manhattan Supreme Court Justice Ronald Zweibel, told The Post that he, too, had a defendant play haircut hooky on Thursday.

“I’ve never heard of this happening before,” Zweibel said of Christopher Rivas, 25, a coke dealer who skipped his sentencing so he could stay in Rikers for a haircut. Rivas is being held in the same building at Rikers as Chatman.

A city correction spokesman said, “We are taking every possible step to ensure it does not happen again. It is both our policy and our number one priority to deliver on-trial inmates on time.”

Kennedy, who has been chatting amiably with her fellow jurors at lunch and break times, returns to the trial Monday.